1. Field of the Invention
The present invention relates to a determination method, an exposure method, a device fabrication method, and a storage medium.
2. Description of the Related Art
An exposure apparatus is employed to fabricate semiconductor devices such as a semiconductor memory and a logic circuit using photolithography. The exposure apparatus projects and transfers a pattern formed on an original (a mask or a reticle) onto a substrate such as a wafer by a projection optical system. To keep up with the recent advances in micropatterning of semiconductor devices, the projection exposure apparatus is required to further improve its resolution (achieve a higher resolution).
Known means for achieving a higher resolution of a projection exposure apparatus are attainment of a higher NA of a projection optical system (an increase in numerical aperture (NA) of the projection optical system), and shortening of the wavelength of exposure light. In addition, nowadays, attainment of a higher NA of a projection optical system by an immersion technique is attracting a great deal of attention. The immersion technique fills the space between a substrate and the final lens (final surface) of a projection optical system with a liquid having a refractive index of 1 or more to increase the NA of the projection optical system in proportion to the refractive index of the liquid. The immersion technique also has the effect of narrowing the incident angle of light which enters a photosensitive agent applied on a substrate to increase the depth of focus in resolution at the same NA.
At the same time, as the NA of a projection optical system increases, it is often the case that light having a wider incident angle enters a substrate (a photosensitive agent (resist) applied on the substrate). This makes it necessary to take account of the incident angle of incident light on the photosensitive agent and the substrate in designing an antireflection coating formed between them. Under the circumstance, Japanese Patent Laid-Open No. 2006-73709 proposes a technique of designing an antireflection coating so as to have low reflectances over the entire incident angle range of light which reaches the photosensitive agent.
Unfortunately, the conventional design of an antireflection coating does not take account of the intensity distribution of light diffracted by an original. This makes it impossible to optimize the structure of the antireflection coating for light beams which have intensities equal to or higher than a threshold in the intensity distribution and therefore mainly contribute to imaging. Thus, an antireflection coating formed based on its conventional design often has a high reflectance for light that mainly contributes to imaging, resulting in degradation in imaging performance.